DESCRIPTION (From the Applicant's Abstract): The major goal of this proposal is to examine the importance of olfactory afferent innervation on the maintenance of the olfactory bulb in adult zebrafish. Plasticity in the adult central nervous system is an important element in recovery from brain injury and disease as well as in learning and memory. An examination of lesion-induced changes after permanent olfactory deafferentation should lead to a better understanding of the normal information that the olfactory bulb receives from the olfactory organ. Olfactory axons have been shown in mammals to influence a variety of features in the olfactory bulb, including expression of proteins. How olfactory axons influence the stabilization of their target in the adult brain is unknown, however. Changes in input to the olfactory bulb, caused by removal of the olfactory afferent axons, will likely result in numerous changes in the brain. This proposal attempts to begin analyzing the mechanisms underlying the interactions between these two structures, with the long-term goal of elucidating cellular and molecular factors involved in stabilization of adult brain organization. Removal of the olfactory organ results in a significant decrease in olfactory bulb volume. This proposal attempts to explain the reason for this reduction, by determining whether there are fewer cells, smaller cells, or higher packing density of cells in the experimentally manipulated bulb.